The present invention relates to a cyclically operated fluid displacement machine.
The present invention can provide a cyclically operated fluid displacement machine either in the form of an engine or a compressor.
The present invention aims to provide a machine which is very simple and in particular which does not require a valve train system, separate alternator and starter motor or cam shaft. The machine of the present invention could be used as an engine in a hybrid vehicle, the engine producing electrical power which would then be used by electrical motors to power the vehicle.
U.S. Pat. No. 5,172,784 describes an arrangement for powering a hybrid vehicle which comprises external combustion Stirling engines coupled to linear generators and used in conjunction with a battery pack to power electric motors for a vehicle.
U.S. Pat. No. 4,924,956 describes a tandem double-acting free piston engine comprising a housing including a cylinder having first and second combustion chambers at opposite ends thereof and a third combustion chamber between the ends. One double acting piston is displaceable between the first and third combustion chamber. A second double acting piston is displaceable between the second and third combustion chambers. The two double acting pistons are linked so that they move in timed relationship with each other. A linear alternator is combined in the engine by attaching one coil to each of the double acting pistons and by surrounding the cylinder with other electrical coils, the fields of which are intersected by the coils on the two pistons.
The present invention provides a cyclically operated fluid displacement machine which comprises:
a housing;
a reciprocating member reciprocal linearly along an axis of reciprocation in the housing and defining with the housing first and second variable volume chambers;
a fluid inlet connected to the first variable volume chamber;
a fluid outlet connected to the second variable volume chamber;
inlet valve means which allows flow of fluid through the fluid inlet into the first variable volume chamber and which prevents flow of fluid from the first variable volume chamber out of the fluid inlet;
transfer valve means which allows flow of fluid from the first variable volume chamber to the second variable volume chamber and which prevents flow of fluid from the second variable volume chamber to the first variable volume chamber;
outlet valve means which allows flow of fluid from the second variable volume chamber out of the fluid outlet and which prevents flow of fluid from the fluid outlet into the second variable volume chamber; wherein:
during movement of the reciprocating member in the housing in a first direction fluid is drawn into the first variable volume chamber and the fluid in the second variable volume chamber expelled from the second variable volume chamber via the fluid outlet; and
during movement of the reciprocating member in the housing in a second direction, opposite to the first direction, fluid is compressed in the first variable volume chamber and fluid is transferred from the first variable volume chamber via the transfer valve means to the second variable volume chamber;
characterised in that:
the reciprocating member comprises a middle section which extends perpendicularly of the axis of reciprocation and two end sections on opposite sides of the middle section, each of the end sections comprising a wall extending generally parallel to the axis of reciprocation and each of the end sections defining with the middle section an open-ended cylinder open at one end;
the housing has a first piston portion which extends into a first of the open-ended cylinders of the reciprocating member and which acts as a piston in the first open-ended cylinder with the first piston portion and the first open-ended cylinder together defining the first variable volume chamber; and
the housing has a second piston portion which extends into a second of the open-ended cylinders of the reciprocating member which acts as a piston in the second open-ended cylinder with the second piston portion and the second open-ended cylinder together defining the second variable volume chamber.
The construction of the machine given above provides an engine or a compressor which has a reduced weight at reduced cost and is simple. In effect, the machine has a single moving member. The machine would be ideal, for instance, for use as an engine in a hybrid vehicle.
Preferably, the reciprocating member has a generally circular radial cross-section and the end sections each comprise an annular wall spaced from a central axis of the reciprocating member.
Making the reciprocating member circular in cross-section eases the manufacture of the machine as a whole.
Preferably, an electrical winding is provided in the housing surrounding the reciprocating member, the electrical winding extending parallel to and adjacent to the end-section walls of the reciprocating member.
The present invention can provide a very compact and simple combined machine and electrical power generator. By locating the winding next to the reciprocating member more power and/or greater electrical control is provided. The construction of the engine can allow the greater percentage of the work of the piston in an engine to be extracted and also the construction of machine allows electrical force to be used efficiently to compress gas in a compressor or to compress fuel/air mixture in an engine. Electrical control can also be used to control the position of the reciprocating member accurately.
Preferably, the electrical winding extends parallel to the axis of reciprocation on the reciprocating member and has a length equivalent to at least the sum of the axial length of the reciprocating member and the distance travelled by the reciprocating member in each reciprocation. This ensures good efficiency.
Preferably the end section walls of the reciprocating member are slidable in slots defined in the housing and the electrical winding in the housing extends adjacent to, and parallel with, surfaces defining the slots. Preferably a seal is formed between the end sections of the reciprocating member and the slots in which the end section slides.
In some embodiments resilient means acts between the housing and the reciprocating member to bias the reciprocating member to move in one direction. Preferably the resilient means act to bias the reciprocating member to reduce the second variable volume chamber to a minimum volume.
The reciprocating member in the present machine is essentially a free motion member. In the prior art, free motion pistons have tended to be used in diesel engines or in Stirling engines. In diesel engines combustion could be ensured by the functioning of the diesel cycle. However, the engines tend to be fairly large and bulky. Stirling engines lack the benefit of internal combustion. The resilient means biassing the reciprocal member could comprise a standard coiled spring or a gas spring. The machine could be configured to work at a frequency equivalent to its resonant frequency, e.g. 3000 rpm. The machine could also be operated by pausing the reciprocating member at a convenient point, with the duration of the pause being variable to vary power output.
Preferably, each of the inlet valve means, the outlet valve means and the transfer valve means comprises either a one-way valve which opens and closes under the action of a pressure differential thereacross or a ported valve comprising a port opening onto one of the variable volume chambers which is cyclically opened and closed by the reciprocating member during reciprocation.
The present invention can remove the need for a complicated valve train system. The present invention when used as an engine can combine an alternator and a starter motor by using electrical winding.
The present invention does away with the need for a cam shaft to control movement of valves. The present invention works essentially on a two-stroke cycle when the invention is used as an engine.
Preferably the inlet valve means comprises a spring-biassed one-way valve.
In one embodiment the machine described before functions as an internal combustion engine, wherein:
a charge of air is drawn into the first variable volume chamber via the fluid inlet;
the charge of air drawn into the first variable volume chamber is compressed;
the compressed charge of air is delivered via the transfer valve means to the second variable volume chamber;
the machine comprises fuel delivery means which delivers fuel to a second variable volume chamber for mixing with the compressed charge of air;
the compressed charge mixture of fuel and air is combusted and allowed to expand in the second variable volume chamber; and
the expanded combusted mixture is scavenged from the second variable volume chamber by a subsequent charge of air delivered to the second variable volume chamber via the transfer valve means.
The present invention provides a very simple construction of engine, with essentially only one moving part.
Preferably the fuel used in the engine is compressed natural gas and the machine comprises storage means for storing natural gas in a pressurised state and fuel delivery means controls the flow of the pressurised natural gas into the second variable volume chamber without use of pumping means. The engine is made simple by the fact that no pump is needed. The engine is made simple and light and can be used for instance to provide enough power to drive a television and lights. Bottled natural gas is widely available. The burning of natural gas solves lots of emission problems, because natural gas burns very efficiently in air without leaving difficult problems of emissions. Indeed it is envisioned that the engine of the present invention will run without any need for treatment of the exhaust gases, for instance without the need of a catalytic converter.
Preferably the inlet valve means comprises a one-way valve, the transfer valve means comprises a port cyclically opened and closed during motion of the reciprocating member and the exhaust valve means comprises a port cyclically opened and closed during motion of the reciprocating member. More preferably, the transfer valve means comprises a first transfer valve which can be opened in the first variable volume chamber and a second transfer port which can be opened in the second variable volume chamber and conduit means extending through the reciprocating member to connect the first and second transfer ports.
The first transfer port is devised in an inwardly facing surface of an end section wall of an open ended cylinder of the reciprocating member and the second transfer port is provided in an inwardly facing surface of an end section wall of the other open ended cylinder of the reciprocating member.
The present invention provides a simple construction wherein the flow of gases passes actually through the reciprocating member itself rather than through the housing surrounding the reciprocating member. This is a novel approach to the passage of gases.
As mentioned above, it is preferable that a first piston portion of the housing extends in a first of the open-ended cylinders and opens and closes the first transfer port present in the first open ended cylinder during reciprocation of the reciprocating member. It is also preferable that a second piston portion of the housing extends in a second of the open-ended cylinders and acts as a piston in the second open ended cylinder and opens and closes the second transfer port present in the second open ended cylinder during reciprocation of the reciprocating member. Ideally, the exhaust valve means comprises an exhaust port which can be opened in the second variable volume chamber and conduit means extending through the reciprocating member to connect the exhaust port to the fluid outlet. The exhaust port provided will be advantageously provided on the inwardly facing surface of the end section wall of the second open ended cylinder, the exhaust port being located opposite the second transfer port. It is preferred that the second piston portion of the housing controls the opening and closing of the exhaust port by opening and closing the exhaust port during reciprocation of the reciprocating member.
It will be appreciated that the engine is simple in construction, operates on a two-stroke cycle and uses scavenging to remove at least some of the combusted gas to exhaust. The scavenging will permit some exhaust gas recirculation, because some exhaust gases will inevitably remain along with the fresh incoming charge, for subsequent combustion. This may improve the emissions of the engine.
Preferably during each reciprocation of the reciprocating member, the second piston portion of the housing sequentially:
opens the exhaust port to allow combusted gases to flow from the second variable volume chamber;
opens the second transfer port to allow admittance of a charge of air into the second variable volume chamber to scavenge combusted gases out of the second variable volume chamber through the exhaust port and to supply air for combustion;
closes the second transfer port to prevent air being expelled through the transfer port during compression; and
closes the exhaust port to seal the second variable volume chamber ready for combustion.
Preferably, the second piston portion of the housing which acts as a piston in the second variable volume chamber is provided with a cut-out portion located adjacent the second transfer port when the second transfer port is open which defines a region where combustion is commenced. Preferably, the fuel delivery means delivers fuel to the region of the second variable volume chamber defined by the cut out portion in the second piston portion of the housing.
Preferably the fuel and air mixture is ignited by active radical combustion. Active radical combustion is a new combustion mechanism recognised in the art in which the fuel/air mixture commences combustion spontaneously due to the presence of free radical ions in the mixture along with an elevated pressure and an elevated temperature of the mixture. The free radical ions are most advantageously introduced by the retention of exhaust gases in the mixture and the use of a two-stroke cycle with scavenging actively assists this. Indeed, the scavenging arrangement preferred in the present invention is a well-proven system which gives a well balanced distribution of fuel/air which is very good for auto ignition. The active radical combustion gives stable and clean combustion, particularly when an engine is run at a steady speed. It is envisaged that the very simple engine of the present invention will use active radical combustion with a two-stroke cycle and will operate as a steady state or a reasonably steady state with perhaps a full load condition and a half-load condition.
The machine of the present invention can be provided with a spark ignition means which operates in the region of the second variable volume chamber when ignition is commenced. The spark ignition means can be used either instead of active radical combustion or in combination with active radical combustion. It is preferred that active radical combustion is used alongside spark ignition, because the spark ignition will ensure combustion at a particular time, whilst the active radical combustion will ensure combustion which provides very low levels of NOx hydrocarbons and carbon monoxide.
Preferably the housing has conduit means passing therethrough which allow cooling air to be drawn from, and expelled to, the atmosphere for passing over and cooling of the reciprocating member. The reciprocating member can itself have cooling passages passing therethrough which allow passage of cooling air through the reciprocating member. Again, the use of air cooling provides a very simple engine, which does not, for instance, require a water pump.
Preferably the engine comprises an electrical winding in the housing surrounding the reciprocating member and the reciprocation of the reciprocating member is used to generate electrical power with the electrical winding being connectable to an electrical load. For instance, the present invention could be used as an engine in a hybrid vehicle. The reciprocating member can generate single phase alternating current. Three-phase alternating current would then be provided by use of an inverter. The present invention integrates the generator into the engine itself by providing an electrical coil in the cylinder liner. The electrical coil is therefore brought very close to the reciprocating member and this aids considerably the efficiency for generators.
The coil is adjacent to the reciprocating member and there is no cylinder liner in between which will attenuate the flux linkage. The clearance between the coil and the reciprocating member can be reduced to perhaps {fraction (1/1000)} th of an inch, ensuring maximum efficiency of the electrical circuit.
The present invention provides a good combination of engine and generator because essentially the engine is turned inside out, with the what would normally be the cylinder block in fact providing the pistons and what would normally be the piston providing the cylinders. This facilitates a good interaction between the reciprocating member and the coil surroundings.
It is envisaged that the present invention would fill the gap between current technology and fuel cell technology and could provide an immediate hybrid power solution for vehicles, where the delay to produce hybrid vehicles has been in part due to the complexity and cost of existing engines and fuel cell systems. The present engine would also be very useful as a static generator. The generator could be used as a generator for electrical power for electrical actuators in a vehicle which are now more common and which are more efficient and more in place of hydraulic actuators. The combined generator engine in a vehicle could be provided with a socket for outside uses so that the engine could not only provide power for powering electric motors driving a vehicle, but also external power, e.g. of 50 Hz, for powering electrical apparatus used outside the vehicle.
The present invention also provides a use of the machine described above in its operation as an engine in which one machine is used in tandem with a second machine, with the reciprocal members of the first and second machines lying on the same axis of reciprocation and with the reciprocal members of the first and second machines connected to move together and with the timing of both machines chosen so that whilst combusted gases are expanded in one machine a charge of fuel and air is being compressed in the other machine. The coupling of the two pistons together would utilise the combustion of fuel and air mixture in one engine with the subsequent expansion of gases as power for compressing charge air in the other engine.
In a further aspect, the machine of the present invention could also be used as a compressor with the reciprocating member driven to reciprocate by electrical power supplied to the electrical winding of the machine, wherein during reciprocation:
the charge of gas is drawn into the first variable volume chamber via the fluid inlet;
a charge of gas drawn into the first variable volume chamber is compressed in the first variable volume chamber;
the compressed gas is delivered via the transfer valve means to the second variable volume chamber;
the compressed gas delivered to the second variable volume chamber is compressed further in the second variable volume chamber;
the compressed gas in the second variable volume chamber is expelled via the outlet means to the outlet.
Preferably the inlet valve means in the compressor embodiment of the invention comprises a first one way valve which allows gas to pass from the fluid inlet into the first variable volume chamber and does not allow gas to pass from the first variable volume chamber out of the fluid inlet, the first one way valve allowing passage of gas from the fluid inlet to the first variable volume chamber only after a pressure differential of a first magnitude is established thereacross.
Preferably the transfer valve means comprises a second one way valve which allows gas to pass from the first variable volume chamber to the second variable volume chamber and which prevents gas flowing from the second variable volume chamber to the first variable volume chamber, the second one way valve allowing passage of gas from the first to the second variable volume chamber only when a pressure differential is established thereacross of a second magnitude.
Preferably the outlet valve means comprises a third one way valve which allows gas to be expelled from the second variable volume chamber to the fluid outlet and prevents gas being drawn into the second variable volume chamber via the fluid outlet, the third one way valve allowing expulsion of gas from the second variable volume chamber only when a pressure differential is established thereacross of a third magnitude.
It will be appreciated that the compressor provided by the invention is a two-stage compressor, with the gas being compressed to a first level of pressure in the first variable volume chamber and the second level of pressure in the second variable volume chamber. Preferably the first, second and third one way valves are spring-biassed valves.
The compressor of the present invention is simple and cheap in construction.
The first variable volume chamber preferably has a cross-section taken perpendicularly of the axis of reciprocation which has a first area and the second variable volume chamber has a cross-section taken radially of the axis of reciprocation which has a second area smaller than the first area. Thus, for a given force on the reciprocating member the pressure applied to gas in the first variable volume chamber is less than the pressure applied to the gas in the second variable volume chamber.
Preferably the housing has a first piston portion which extends into the first variable volume chamber and matches in radial cross-section the first variable volume chamber and the housing has a second piston portion which extends into the second variable volume chamber and matches in radial cross-section the second variable volume chamber.
The present invention achieves its simplicity of construction by reversing the usual arrangement of components. The cylinders are provided by the reciprocating member and the pistons are provided by the static housing.
Preferably the inlet valve means is provided in the first piston portion of the housing and the outlet valve means is provided in the second piston portion. Preferably the transfer valve means is located in the middle section of the reciprocating member.
It is preferred that the second variable volume chamber has a maximum volume smaller than the maximum volume of the first variable volume chamber.
Preferably the engine has control means to control the electrical wave form used to power the electrical winding and thereby control the output of the machine.